1. Field of the Invention
This invention pertains to hydraulic compression apparatus and more particularly to hydraulic compression apparatus used in hand operated, hydraulic compression tools adapted for compressing an electrical connector about a conductor.
2. Description of the Prior Art
A number of hydraulic compression apparatus have been developed for various needs. One of these needs is for use in a compression tool for compressing metal connectors about electrical conductors to form an electrical and structural connection between two conductors.
Conventional tools such as that shown in the patent issued to McDurmont issued Nov. 3, 1964, U.S. Pat. No. 3,154,981, show a hand operated hydraulic compression tool having two operating levers. As in most hydraulic tools one of the operating levers is rigidly fixed to the hydraulic section of the tool. Connected also to the hydraulic section is a movable, second lever which is joined to the pump plunger and is used to create a vacuum to draw and compress hydraulic fluid, or oil, for the operation of the tool. Because of the single, movable lever arrangement in traditional tools the force exerted on the pump plunger is limited by the force applied to the end of the single, movable lever multiplied by the mechanical advantage of the lever linkage. This means that the pump plunger must be of a small diameter to be operatable under the force applied by the lever and thus will compress smaller volumes of the reservoir fluid. Generally, the smaller the volume of fluid compressed, the smaller the incremental distance of travel of the tool compression head. In traditional tools this arrangement of a small lever force and small pump plunger diameter required many strokes of the handle lever to advance the tool head and complete a compression connection. Thus, to complete a single compression, or crimp, of a workpiece held in the tool head, multiple operations of the handle were required and a substantial amount of time for each crimp was used.
In the past, to remedy this situation some conventional tools utilized a rapid advance system. This rapid advance system comprised generally a means by which the reservoir fluid could be rapidly compressed, forcing fluid through the various compression chambers and rapidly advancing the tool head to the point where it first experienced resistance from the work piece. One such type of rapid advance system would use a plunger having two stepped portions, one having a smaller diameter than the other. When operated, both stepped portions of the plunger would operate to compell larger volumes of fluid towards the compression piston and thereby more rapidly advance the compression head until it met resistance from the workpiece to be compressed. When the compression head met resistance from the workpiece, only the smaller diameter, stepped portion would then operate to compress relatively smaller volumes of fluid and thus advance the tool head in relatively smaller increments.
In another rapid advance system one of the operating levers (generally the rigid lever) would be in threaded association with the fluid reservoir and would be turned to advance the fluid through the hydraulic system and compress the tool head until resistance from the workpiece was met.
Both types of systems for rapid advance of the tool head required extra, multiple parts for their operation. These extra parts added weight to the tool and increased its complexity. Due in part to these extra parts, conventional hydraulic tools weighed eleven or twelve pounds. Since these tools are used for long periods of time and often at uncomfortable angles by an operator the weight of the tool is of substantial importance.
Compression tools, to be operative, need a pressure relief valve to indicate to the operator when the required compression had been completed. This avoids over compressing the workpiece and straining the metal parts of the tool. Also, conventional tools require a means by which to return hydraulic fluid back to the reservoir after a compression has been completed, to ready the tool for another compression. Conventional tools required separate porting and parts for each of these functions. For example for the pressure relief system conventional tools would have a relief valve seat and pin with an additional seating ball and porting. For the return of fluid to the reservoir, conventional tools would have a toggle release arrangement or a release integral with a portion of the handle which when twisted would compress a ball in a ball seat to allow the oil to return to the reservoir. The separation of these two functions in conventional tools required additional parts, with additional assembly requirements and associated additional weight.
It is desirable in most compression tools to measure from time to time the maximum pressure exerted by the tool head on a workpiece before the relief valve assembly becomes operative. Some prior art tools have adapters for attaching a pressure gauge to the hydraulic section of the tool to read the maximum pressure. These adapters generally require extra porting of the pump block and additional valves and springs. These assemblies also add complexity to the tool and extra weight.
Many prior art hydraulic apparatus require the maintenance of a minimum volume of hydraulic fluid in two separate reservoirs in the tool, one is a supply reservoir from which fluid is drawn to be compressed. The other is a compression reservoir into which the fluid drawn from the supply reservoir is compressed. This increases the volume of the compression reservoir and forces the movement of a mechanical piece. The requirement of two separate reservoirs increases the weight and complexity of the tool and provides a risk that contaminent to either reservoir will impair operation of the apparatus.
Thus, there is a need in the field for a hand held compression apparatus in which the handle lever arrangement allows a relatively large degree of force to be exerted on the plunger and thereby allows the use of a large diameter plunger to compress relatively large volumes of hydraulic fluid per each compression stroke. Further, there is further a need in the field for a compression apparatus which will advance the tool head in relatively large increments to complete a compression without the need of a separate, rapid advance system. Further, there is a need in the field for a compression apparatus which will complete a compression of a workpiece with a minimum number of compression strokes of the operating levers. Further, there is a need in the field for a compression tool which is lightweight, easy to assemble and maintain and has relatively few moving parts. There is a further need in the field for a compression apparatus in which the pressure relief mechanism is integral with the oil return mechanism thereby eliminating the need for separate porting and separate parts for each of these functions. There is a need in the field for a compression tool which has an adapter assembly therein for the attachment of a pressure gauge where said adapter assembly requies few additional parts. There is also a need for a compression apparatus that does not require the maintenance of two separate reservoirs of hydraulic fluid each having a necessary constant minimum volume requirement.